My question is why do they believe this? It seems to be a relatively recent development among the religious outside of the Catholic Church. What's the scriptural basis for such a position?
What if he decides not to cover genetic diseases because they're God's will?

What if he decides not to pay them as much as they want? What if he decides not to provide insurance? Well, he cannot do that because we already force him to do that. I think he should be able to offer any compensation he does or does not want to and perspective employees are welcome to not work for him.